This invention relates to a retractable insulated canopy for greenhouses.
Up to 90% of the heat loss from conventional greenhouses occurs at night and during other dark or overcast periods. Accordingly, some greenhouses presently employ a variety of conventional insulating mats, shades, curtains and heat blankets for covering the transparent panes of the greenhouse and thereby slowing the escape of heat during periods of darkness. See, for example, U.S. Pat. No. 4,318,251. Such devices are also used to regulate the amount of sunlight entering the greenhouse and thereby the flowering cycles of certain plants.
The effectiveness of such insulating shades has been limited. At insulation levels above approximately R-4 these devices are too thick, bulky and cumbersome to withdraw and deploy each day. Interior supports and obstructions in greenhouses leave spaces in blankets that are difficult to seal against air infiltration and heat loss. Hand operated roll-down shades or blankets have been used on the outside of small greenhouses but like interior blankets their R-value is low because thick insulation is difficult to operate on a day to day basis.
There has been no practical system to employ power operated blankets that roll up and down for commercial greenhouses especially in stormy weather when insulated is most needed. Double layers of fixed plastic, inflated with air are used, with insulation values of R-3 but these systems cut the sunlight admitted into greenhouses by over 50%, and as a result cut plant growth in half in the winter months.
Moreover, existing greenhouse shades and curtains also permit a significant portion of the solar radiation passing in the vicinity of the greenhouse to totally miss the house. Such radiation and its energy is, therefore, not utilized.
High energy costs and inefficient heating have severely hampered most of the large commercial greenhouses in the frost belt of the United States. The average consumption of oil for such greenhouses is typically two gallons per square foot per year. As a result the market in plants and cut flowers has been largely assumed by foreign growers. By employing an enhanced system of heavy insulation during the night, greenhouse oil consumption could be cut by 80-90% thereby making U.S. growers more competitive.
To address these problems I have previously provided an insulated greenhouse canopy apparatus which employs a rigid self supporting enclosure, U.S. Ser. No. 717,900, filed Mar. 29, 1985. Although that structure provides improved results it is rather heavy because it employs a rigid self supporting construction. As a result, raising and lowering the canopy can be difficult at times. The system also requires a rather complex system of winches and cables for raising and lowering the canopy.